1. Field of Invention
The present invention relates to a package structure, and more particularly to a light emitting diode (LED) package structure of a package type in which light emitting elements do not directly contact a fluorescent material.
2. Related Art
Due to low power consumption, high efficiency, and long life, LEDs are widely used in various application fields, for example, as light sources for backlight modules of notebook computers, monitors, mobile phones, TV sets, and liquid crystal displays (LCDs). Moreover, as more and more researchers work on the research and development of the LEDs, the luminous intensity of the LEDs already reaches a lighting level for daily life at present.
For example, the most commonly used white LED modulates and combines red, green, and blue light, in which the LED chips that emit red, green, and blue light are combined in a form of array and packaged. Color lights emitted by the LEDs of the three colors are mixed, so as to obtain a multi-chip LED package device capable of emitting white light.
The conventional LED package device uses a package having a phosphor powder added therein to directly cover the LED chips, that is, the LEDs directly contact and join the phosphor powder for refracting the light. In the conventional method, the phosphor powder is uniformly mixed into the package of a resin material (referred to as uniform distribution) or a mixing region of the phosphor powder is close to a position of the LED chip (referred to as conformal distribution), so as to improve the light color uniformity of the LEDs.
Thus, when the LED chip is in operation, the generated high heat energy will be directly transferred to the package material, and the properties of the phosphor powder change when being heated, resulting in decrease of the overall luminance performance of the LED package device. Moreover, the current LED package techniques cannot achieve the consistency of the spatial spectral distribution and the illumination brightness of the illuminating light.
At present, as the luminous efficiency of the conventional LED is still too low, and the manufacturing cost is relatively high, it is a very important subject to significantly improve the luminous efficiency of the LED and reduce the manufacturing cost of the LED for the research and development personnel in the related field, so as to enhance competitiveness of the LED in the future.
Package technique is one of the import facts that affect the performance of the LED, and in order to improve color uniformity of the LED and achieve high lumen output (light flux), the conventional phosphor powder coating method cannot meet the current requirements of the LED. Therefore, manufacturers have developed a phosphor powder coating method different from the conventional method, for example, the technique recorded in U.S. Pat. No. 6,576,488 (referred to as Patent '488 hereinafter), in which the LED is manufactured by depositing a phosphor layer on a conductive substrate/non-conductive substrate (chip) through electrophoretic coating or by directly attaching a phosphor coated sheet on the chip, so as to improve the luminance performance of the LED.
However, the electrophoretic coating technique disclosed in Patent '488 has the disadvantage of expensive manufacturing cost, so the cost of the LED cannot be reduced, and thus the LED manufactured through this method does not have a price advantage on the market. Furthermore, in the method of attaching the phosphor coated sheet on the chip, the preparation process is complicated as the phosphor coated sheet has to be manufactured additionally; moreover, the step of attaching the phosphor coated sheet must be very accurate, so the yield cannot be controlled, thus resulting in increase of the manufacturing cost.
At present, some manufacturers use a silicone lens as the package material of the LED, so as to increase the index of refraction of the LED, and thereby improving the luminance performance of the LED. In addition to the advantages of high light transmission and high index of refraction, the silicone lens further has excellent properties such as high temperature resistance, high insulation, and high chemical stability, and therefore the silicone lens can be used in the high power LEDs suitably. The silicone lens can endure the high temperature generated during operation of the LED, such that the problem that the conventional package material deteriorates due to high temperature is solved, and the reliability of the LED is significantly improved.